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Systematics of Indo-Pacific Philippia (Psilaxis), Architectonicid Gastropods with Eggs and Young in the Umbilicus

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Title:Systematics of Indo-Pacific Philippia (Psilaxis), Architectonicid Gastropods with Eggs and Young in the Umbilicus
Authors:Robertson, Robert
Date Issued:Jan 1970
Publisher:University of Hawai'i Press
Citation:Robertson R. 1970. Systematics of Indo-Pacific Philippia (Psilaxis), architectonicid gastropods with eggs and young in the umbilicus. Pac Sci 24(1): 66-83.
Abstract:The subgenus Psilaxis Woodring is distinguished from Philippia
Gray, s.s., on the basis of differences in the shells, jaws, opercula, and doubtfully
radulae. Only two species of Psilaxis, differing mainly in three protoconch characters,
are recognized in the Indo-Pacific. Philippia (Psilaxis) radiata (Roding),
with the generally smaller protoconch, is the most abundant and widespread species,
ranging from South Africa and the Red Sea east to the Marquesas and the
Hawaiian Islands ; it is thus both tropical and subtropical. Philippia (Psilaxis)
oxytropis A. Adams has a larger protoconch and a disjunct range, being known
only from the subtropical western and central Pacific Ocean-including Japan, the
Hawaiian Islands, and New Zealand but excluding latitudes between 20 ° Nand
20 ° S. Young postlarval P. oxytropis live in the umbilicus of the adult shells,
and in P. radiata one egg mass has been found in an umbilicus. Nevertheless it
is concluded from the small egg size of P. radiata (average diameter 63μ) that
both species have a long pelagic larval stage. Philippia hybrida (Linn.) is a
Mediterranean species in the subgenus Philippia, s.s., and P. layardi A. Adams is
a synonym of P. radiata. In Marqu esan P. radiata there is a noteworthy increase
and bimodality in protoconch size that are attributed tentatively (with no chromosomal
evidence) to polyploidy. Polyploidy perhaps also is involved in the origin
of species of Philipp ia and in the origin of Psilaxis from Philippia, s.s. By the
Miocene, Psilaxis seems to have displaced Philippia, s.s., from most areas except
peripherally in the subtropics. The pyramidellid-like egg capsules of architectonicids
are described for the first time, and the larvae are also opisthobranch-like.
Philippia has a cuticularized esophageal tube and radular teeth similar ( analogous? )
to those in the Epitoniidae.
Appears in Collections: Pacific Science Volume 24, Number 1, 1970

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